1. Field of the Invention
This invention relates to a method and apparatus for aligning a contact mask with an irregularly shaped object intolerant of contact during alignment. In particular, an apparatus and process for aligning a contact mask with a semiconductor memory cube is described.
2. Background Information
Computer memories have achieved greater and greater density as the computer industry has matured. Traditionally, these memories are created on a semiconductor wafer and then diced into individual memory chips. Input/Output (I/O) connections between chip and package are made using wire bond or solder ball technologies or other well-known processes. A description of solder ball technology can found in U.S. Pat. Nos. 3,429,040 and 3,401,126 which are assigned to the Assignee of this invention.
To achieve even greater packaging density for semiconductor components, it is known that individual chips can be laminated together. Additional information on this technology can be found in IBM Technical Disclosure Bulletin, Vol. 18, NO. 10, March 1976, pp. 3239-3242 and in U.S. Pat. Nos. 4,551,629 and 4,646,128. With this arrangement, it is no longer possible to make I/O connections on the top surfaces of the chips because they are no longer accessible. Therefore, it is required to make I/O connections along the exposed perimeters of the individual chips.
FIG. 1 shows a diagram of a memory cube 10 made up of individual chips 12 laminated together. One surface of the cube 14, which is made up of the edge surfaces of a common side of the chips 12, serves as the I/O surface for the package. When depositing the metallurgy for I/O connection using solder ball technology, there is one step in the process where a contact mask 20 as shown in FIG. 2 must be aligned with the pattern of connection sites on the memory cube without any touching of the surface. Then, the contact mask is clamped to the cube in a fixture for further processing. The surface of the memory cube is absolutely intolerant of any sliding friction during this alignment and clamping procedure, since the metal previously deposited could be damaged.
Conventional mask alignment tools cannot meet this requirement since they allow a contact mask to slide on top of a wafer or other object in process during the alignment. Additionally, conventional tooling is not adapted to handle non-wafer shaped structure, such as a cube. Therefore, it is desirable to have an apparatus and method for aligning a contact mask and a non-wafer shaped structure, such as a memory cube, without the two touching until alignment is completed. At the point, contact is permitted and the objects can be clamped together for further processing steps, such as metal deposition.